Stepwise-operating power apparatus

ABSTRACT

Hydraulic power apparatus operating stepwise and comprising essentially a body having arranged therein a fixed retaining device, an annular piston and a movable traction device connected to the tubular rod of said piston, said fixed retaining device and said movable traction device comprising clamping members adapted to grip and release by turn cables, rods or the like, the clamping members of one device gripping the cables when the clamping members of the other device release said cables, and vice-versa. The invention may be used either as a traction ram when it is held in a fixed position for exerting a tractive effort, for example on a cable for prestressing a concrete mass, or as a &#39;&#39;&#39;&#39;re-advancing&#39;&#39;&#39;&#39; device for displacing step-by-step a mass or load to which it is connected along a rail-forming cable or rod.

[S4] STEPWISE-OPERATING POWER APPARATUS [451 Apr. 4, 1972 PrimaryExaminerOthell M. Simpson Attorney-Amster & Rothstein [72] Inventor:Rene Bechl, Bois Colombes, France [73] Assignee: Soclete des Grands,Travaux de Marseille, [57] ABSTRACT France Hydraulic power apparatusoperating stepwise and comprising [22] Filed. on. 23 1970 essentially abody having arranged therein a fixed retaining device, an annular pistonand a movable traction device con- [2l] Appl. No 83,534 nected to thetubular rod of said piston, said fixed retaining device and said movabletraction device comprising clamping members adapted to grip and releaseby turn cables, rods or E CCll. the like, the p g members of one deviceg pp g the cm 58] g i 4/68 29 A bles when the clamping members of theother device release o 'T said cables, and vice-versa. The invention maybe used either as a traction ram when it is held in a fixed position forexerting [56] References Cited a tractive effort, for example on a cablefor prestressing a UNITED STATES PATENTS concrete mass, or as are-advancing? device for displacing step-by-step a mass or load to whichit IS connected along a 3,338,553 8/ l 967 Perslcke ..254/29 A il f icable or 3,35l,320 11/1967 Harvey ..254/29 A 3,399,865 9/1968 Kelly..254/29 A 9'Clalms, 8 Drawing Figures 21a 1 2 11 10 12 Y/ 4 v 1 16 13ais 2 7a 5" E 1 h L 1 w v a r WM '*ll| I! #1 H 92"9- Q. P 5 \g 7 f a 1* 2ll, -l F t/I glam l'" 1 a; s"

a a I a e 6 a "w x I lie I 15 16a $3 16b 15 hr x PATENTEDAPR 4l9723,653,634

sum 2 OF 3 a F1.g.2.

5 A M m ms/vs'asaw glam Mam/70R.

STEPWISE-OPERATING POWER APPARATUS BACKGROUND OF THE INVENTION Thisinvention relates to a power apparatus adapted to generate a relativedisplacement between an elongated member of constant cross-sectionalarea, on the one hand, and itself, or a mass to which it is connected onthe other hand.

This invention is concerned more particularly with a traction ramadapted, when held in a fixed position, to exert a tractive effort on atleast one elongated member of constant cross-sectional area, for examplea cable for prestressing concrete.

In the specific example of the prestressing of a concrete beam, aconsiderable tractive force is applied to one end of at least one cableor rope of which the opposite end is anchored to one end of the beam tobe prestressed, this cable following a predetermined path within saidbeam. To this end, a traction unit is used as a rule, this unit beingmounted to the first aforesaid cable end and connected directly orindirectly to the piston of a power ram. In conventional tractive unitsof this character, such as the one disclosed in the French Pat. No.l.530,660, the tractive effort is applied to the cable at one go, sothat the stroke of the piston of the traction ram must necessarily be atleast equal to the desired elongation of the cable to which the tractiveeffort is applied. Now the cable elongation is an increasing function ofthe cable length and also of the intensity of the tractive force towhich it is submitted, so that when it is contemplated to prestressbeams of relatively great length the cable elongation may be of theorder of 40 or more. As a result, according to the length of the beamsto be prestressed, there must be provided either several traction ramsof different lengths, thus compelling acontractor specialized inprestressing works to have a complete range of rams having differentlengths, or a single ram but of considerable length, which in this caseconstitutes an extremely long and cumbersome device difficult to handlein case of prestressing operations requiring a relatively reduced cableelongation.

SUMMARY OF THE INVENTION It is the essential scope ofthe'present-invention to avoid these inconveniences by providing atraction ram or relatively reduced length, permitting of prestressingbeams of any desired length.

The present invention is also concerned with a power apparatus, notablya traction ram, operating stepwise, as will be explained hereinafter.

Furthermore, the invention is concerned with a power apparatus capableof generating a relative step-by-step movement between an elongatedmember of constant cross sectional area, on the one hand, and thisapparatus or a mass to which said apparatus is connected, on the otherhand.

To this end, the power apparatus operating stepwise according to thisinvention is characterized in that it comprises a body formed with acylindrical bore, a retaining device secured by one of its ends to saidbody, in a coaxial position in said bore of said body, and having acylindrical surface of smaller diameter than said bore, so as to providebetween its external surface and the wall of said bore an annular spaceclosed at the end of the retaining device which is secured to said body,an annular piston adapted to slide axially in said annular space so asto form therein two axially spaced annular chambers each provided withan inlet port for introducing a fluid under pressure into the relevantchamber, a tubular coaxial piston rod having one end connected to saidannular piston and extending from said piston in the direction oppositeto said closed end of said annular space, a sealing member disposedbetween the inner wall of the bore of said body and the external surfaceof the tubular piston rod for closing in a fluid-tight manner the otherend of said annular space, and a movable traction device positioned inalignment with said fixed retaining device and connected to the otherend of the tubular piston rod, the fixed retaining device and themovable traction device being adapted to receive therethrough, in theaxial direction, at least one elongated member of constantcross-sectional area, with which the power apparatus is adapted toco-act, and enclosing each a plurality of clamping members co-acting byfrictional contact with said elongated member, for automaticallyreleasing and re-gripping said elongated member when a fluid underpressure is directed into one of said two annular chambers and when thepiston is moved in a first direction corresponding to a power stroke, soas to generate a relative displacement between the power apparatus andsaid elongated member, and, vice-versa, for automatically gripping andreleasing said elongated member when fluid under pressure is fed intothe other annular chamber and the piston is moved in a directionopposite to said first direction, which corresponds to an inoperativepiston stroke.

Thus, the power apparatus according to the present invention can beutilized either as a traction ram when it is held in a fixed positionfor exerting a tractive effort on at least one elongated member ofconstant cross-sectional sectional area, for example a cable forprestressing concrete or any other material, or as a driving device orre-advancer" for displacing stepwise or step-by-step a mass to which itis connected, for example a cable or a rail-forming bar. In this lastinstance, the power apparatus according to this invention isparticularly suited for all applications in which it is desired toproduce the step-by-step, slow and accurate movement of a considerablemass.

In case the power apparatus according to this invention were intendedmore particularly for use as a traction ram for prestressing concretebeams, it is clear that it can be designed with a view to produce arelatively short piston stroke and, therefore, have a total length alsorelatively short, since it is adapted to operate stepwise or, in otherwords, by causing its movable traction device and its fixed retainingdevice to coact by turns with the traction cable or cables in order topull them and then retain said cable or cables in the position obtainedafter said pulling action, during the power or operative and inoperativestrokes of the piston, r,espectively. In spite of the moderate length ofthe apparatus of this invention, it is thus advantageously possible toprestress beams of any desired length, since it is only necessary toactuate its piston a certain numberof times, in either direction, untilthe desired degree of prestress is obtained.

BRlEF DESCRIPTION OF THE DRAWING Now a typical form of embodiment of thepresent invention will be described by way of example with reference tothe accompanying drawings, in which:

FIG. 1 is a longitudinal section showing a stepwise-operating powerapparatus according to the present invention, designed more particularlyfor use as a traction ram in the prestressing of concrete elements, thisview showing in its upper portion and its lower portion respectively twopositions of operation of the component elements of the traction ram;

FIG. 2 is a cross section taken along the line IIII of H0. 1;

FIG. 3 is a section taken along the line IIIIII of FIG. 1 showing on alarger scale clamping members of the traction ram according to thisinvention;

FIG. 4 is a section taken along the line IV-IV of HG. 3;

FIG. 5 is a detail view showing a component element of the clampingmembers illustrated in FIGS. 3 and 4;

FIGS. 6, 7 and 8 are fragmentary diagrammatic views showing in axialsection the traction ram of this invention for illustrating the variousstages of its operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

The traction ram 1 illustrated in the drawings is intended moreparticularly for use in the operation consisting in prestressing aconcrete member, for example a concrete beam 2, of which only one end isshown in FIG. 1. To this end, the beam 2 has embedded therein, thelongitudinal direction and along a suitable path, a tube 3 havingsecured to one end a bearing plate 4 engageable by the ram 1. This tube3 permits the passage of at least one cable 5 having one end (not shown)connected in the conventional manner to device (not shown) bearingagainst the opposite end of beam 2. In the example illustrated sevencables 5 are provided and constitute either separate cables or theelementary strands of a same cable. Secured in a conventional manner tothe cables 5 is a substantially cylindrical anchoring device 6 having ascrew-threaded external surface; when the cables 5 are in theirinoperative condition, this anchoring device 6 is somewhat engaged intothe tube 3. As in the structure of conventional traction rams designedfor prestressing a concrete beam, the traction ram according to thisinvention bears against said bearing plate 4 through the medium of anintermediate bearing member 7, for pulling the cables 5 and thuselongate same as a consequence of the traction force exerted thereon,whereby the anchoring device 6 is eventually positioned within thebearing plate 4 (FIG. 1 A nut 8 previously engaged on the cables 5 maythen be screwed on the anchoring device 6 until it bears against theplate 4 for holding the cables 5 in their taut condition, as alreadyknown in the art.

According to an essential feature characterizing this invention thetraction ram 1 operates by successive steps; in other words, it isadapted to pull the cables 5 according to a cycle comprising alternatingtraction phases and inoperative return phases during which however thecables are retained in the position obtained during the precedingtraction phase. To this end, the traction ram according to thisinvention comprises essentially a substantially cylindrical body 10having mounted concentrically therein a fixed retaining device 11, anannular piston 12 and a movable traction device 13 connected to thetubular rod 14 of annular piston 12. The fixed retaining device 11 andthe movable traction device 13 incorporate similar clamping members 15to be described more in detail presently, these devices being adapted toalternatively grip and release the cables 5; to this end, the cables 5are gripped by the clamping members 15 of the movable traction device 13when the clamping members 15 of the fixed retaining device 11 releasethem, and vice-versa. The cylindrical body 10 of traction ram 1comprises a cylindrical concentric bore 10a internally screw-threaded ateither end, and the member 7 through which the body 10 engages thebearing plate 4 con sists of a tubular member having one end formed withinner and outer screw threads so that on the one hand it can be screwedinto the end of body 10 adjacent the beam 2 and, on the other hand, itcan receive the screw-threaded end of the fixed retaining device 11. Theintermediate bearing member 7 further comprises a pair of longitudinalapertures 7a through which access may be had to the nut 8 for tighteningsame to the anchoring device 6. In order to facilitate the actuation ofthis nut 8 the latter has preferably a cylindrical outer configurationwith a pair of flat faces 8a engageable by corresponding flat portionsof a control socket 9 formed with radial holes 9a adapted to receive thestuds of a tightening spanner (not shown).

The fixed retaining device 11 secured in the manner explainedhereinabove to the intermediate bearing member 7 is thus rigid with thebody 10 of the traction ram. Moreover, its body 11a is of cylindricalexternal configuration and extends coaxially within the bore 100 so asto provide between its peripheral surface and the inner wall of saidbore 100 an annular space 16 in which an annular piston 12 is adapted toslide. This annular piston 12 divides the annular space 16 into twoaxially spaced chambers 16a and 16b; an orifice for introducing fluidunder pressure opens into each chamber. These two orifices 17 and 18 areformed respectively through the wall of the cylindrical body 10 of thetraction ram and communicate through suitable ducts and pipe lines and adistributor (not shown) with a source of fluid under pressure (also notshown). The tubular piston rod 14 sliding with piston 12 on the outercylindrical surface of the body 11a of the fixed retaining device 11extends into the chamber 16b beyond the aforesaid fixed retaining device11. In the end portion of cylindrical body 10 which is opposite to theconcrete beam 2 an annular plug 19 is screwed for closing in afluid-tight manner the chamber 16b and acting as a rear abutment memberto said annular piston 12. The end of said tubular piston rod 14 (whichis opposite to piston 12) is formed with an internally screw-threadedportion adapted to engage a corresponding externally screw-threadedcylindrical portion of the body 130 of said movable traction device 13.Thus, the movable traction device 13 is aligned with the fixed retainingdevice 11 and moves bodily with the annular piston 12.

The body 11a of the fixed retaining device 11 and the body 13a of themovable traction device 13 are both formed with an axial bore shaped toprovide a certain gradient in order to coact with the external surfaceof the clamping members 15 formed with a similar or correspondinggradient. This gradient is so designed that when the clamping membersare moved in relation to their respective bores formed in said bodiesand 130, as a result of the frictional contact between the cables 5 andthe clamping members, in combination with the movement of said body 13aas a consequence of the thrust of piston 12, said clamping members gripthe cables when the formers are moved in the direction of the arrow F(FIG. 1) in relation to the relevant bodies 11a and 13a, and move awayfrom said cables, so as to release same, when said clamping members movein the opposite axial direction shown by the arrow F in FIG. 1 inrelation to the same bodies 11a and 13a.

In order to reduce the outer diameter of these bodies 110 and 13a, it isparticularly advantageous that the inclined surfaces of the bores formedin these bodies, as well as the corresponding inclined surfaces formedon clamping members 15, be shaped somewhat in the fashion of inner andouter threads respectively, each thread comprising a front face 20a ofrelatively great width with a moderate inclination to the axis of theassembly, and a rear face 20b of considerably shorter width and greaterinclination in relation to said axis than the front face 20a. Thissurface may advantageously be machined in the relevant bores of bodies110 and by using a lathe, exactly as in the machining of internal screwthreads.

Now the shape of the clamping members 15 of the fixed retaining device11 and of the movable traction device 13 will be described more indetail, together with the manner in which these members can be obtained,with reference to FIGS. 3 and 4 illustrating these members on a largerscale. The clamping members 15 comprise a number of keys 15a to 15g(equal in number to the number of cables 5 to be gripped) havingsubstantially the shape of cylinder sectors and which, when assembled asshown in FIG. 3, constitute an assembly of substantially cylindricalconfiguration formed with radial slots 21 extending throughout itslength. Moreover, in the lateral faces of these keys 15a to 153determining said radial slots 21, longitudinal grooves 22 having asemi-circular cross-section are formed; these grooves are adapted tosurround by pairs of cable 5 of which they accommodate the major portionof the peripheral surface. The ends of grooves 22 adjacent to theconcrete beam 2 are bevelled as shown at 22a in FIG. 4, in order tofacilitate the positioning of the cables. To obtain these keys 15a to15g and give the afore-mentioned screw thread appearance to the outersurface of the assembly constituted by these keys with the front faces20a and the rear faces 20b, the following procedure may advantageouslybe adhered to. It is only necessary to start from a cylindrical blockand form on its outer surface, for example on a lathe, the above-definedspecial screw-threads. Upon completion of the external screws, thecentral hole 23 is drilled and the assembly is cut into sectors. Thefaces of each sector are then milled to form the holes 24 permitting thepassage of the strands or cables 5. This machining method is moreaccurate than the drilling performed before cutting the block intosectors. Of course, the number of holes 24 must be be equal to thenumber of cables with which the traction device is intended toco-operate. Then the cylindrical block is cut along planes containingthe axis of the block nd also the axis of each hole 24, so as to obtainthe keys 15a to 15g having substantially the shape of cylinder sectors,each hole 24 forming in the parallel adjacent faces of two keys thelongitudinalgrooves with semicircular cross-sectional contour of thesekeys.

In order to keep the keys properlyspaced from one another and facilitatethe positioning of cables 5 in said holes 24, and also the release ofthese cables by said keys, there is provided according to a specificfeature of the present invention a set of elastic return members eachbearing against two lateral parallel registering faces of two adjacentkeys. In the preferred from of embodiment of, the present invention eachelastic return member may advantageously consist of a spring steel blade25 of corrugated configuration so that the peak of its corrugationsbears by turns on the lateral parallel registering faces of two adjacentkeys parallel to their grooves 22, between these grooves and the keyedge parallel to their peripheral surface. In order to hold the blades25against axial movement in their relevant grooves 26, these blades arebent at one end so as to form a stop lug 25a engageable into a hole 26aformed in the bottom of said grooves 26.

Referring again to the construction of FIGS. 1 and 2, it will be seenthat the traction ram 1 according to the present invention is adapted tobe suspended from any suitable supporting device by means of a collar 27comprised of two semi-circular members 27a, 27b assembled by bolts andnuts 28. Moreover, two grids 29 and 30, having a function to beexplained presently, are provided; these grids comprise countersunk orbevelled holes 29a and 30a, respectively, aligned with the holes 24 ofclamping members 15. The grid 29is secured to the end of'the fixedretaining device 11 which is adjacent .to the movable traction device13, and the grid 30 is normally adapted to move freely between the nut 8and the end of the fixed retaining device which is adjacent to theconcrete beam 2. Two lock pegs 31 may be inserted into transverse holes32 drilled through the intermediate'bearing member 7 for holding thegrid 30 in contact with the end of the clamping members 15 of the.retaining device ll, so that the rear faces 20b of the threads formedon said clamping members 15 can bear against the corresponding faces ofthe female threads of block 11a, as shown in the lower portion ofFIG. 1. In this position the keys lower portion of FIG. 1 and clampthese cables. During this clamping action, the piston 12 and movabletraction block 13 move along a distance d, without exerting anyefficient tractive effort on the cables 5. This stroke d 'IFIG. 1)corresponds substantially to the relative movement of keys with respectto the body 13a of traction device 13. When va sufficient clampingaction is produced, the movable traction block 13 carries along its keys15 with pull the cables 5 so as to elongate them in the direction of thearrow F,. Meanwhile, the cables 5 carry along by frictional contact thekeys 15 of the fixed retaining device 11 in thedirection of the arrow Finorder to move them to the release position if they are not already inthis position. This positive traction stroke takes place until theannular piston 12 engages the plug 19. The various component elements ofthe ram are then in the position illustrated in FIG. 7. If from thisposition the pressure is released in chamber 16a and fluid underpressure is fed to chamber 161: through orifice 18, the piston 12. andthe movable traction block 13 will move firstly'through a distance d, inthe direction of the arrow F and, during this stroke, the cables 5 arepartially slackened and carry along, by frictional contact, the keys 15of retaining device 11, so that these keys will move to the positionillustrated in'FIG. 8 was to clamp and hold the cables 5 in the tautposition. The stroke 11;, substantially equal to stroke d corresponds toa slight loss of tension in the cables 5 and to a very moderate loss ofuseful stroke of piston 12. From the position illustrated in FIG. 8, inwhich the cables 5 are of the fixed retaining device 11 are released.Similarly, when the keys of the movable traction device 13 are in theposition illustrated in the upper portion of FIG. l,- they are alsoreleased. I

Now, reference will be made to FIG. 1 andalso to FIGS. 6, 7 and 8fordescribing the manner in which the traction ram 1 of this invention canbe positioned on the cables 5, and its mode of operation. Firstly, inorder to ascertain whether the holes 24 of the various clamping membersand the holes'of the grids are properly aligned, the operators insert atleast two rigid aligning bars into these holes, and-these are thusre-aligned, if necessary. While maintaining these aligning bars in saidholes of the clamping members and grids, the traction ram 1 is broughtto a position adjacent the ends of cables 5 which emerge from theopening of bearing plate 4. Having previously slipped the nut 8.0n thesecables 5, the ends of the cables 15 are subsequently inserted insuccession into the holes of grid 30, into the holes of the clampingmembers of the fixed retaining device 11, into those of grid 29 andfinally into those of the movable traction device 13, so as to push backthe aligning bars and permit their removal. The ram is then appliedagainst the bearing plate 4 and the pegs 21 areremoved, in case they arestill positioned in the device, so thatthe grid 30 can move freely alongthe cables between the device 11 and nut 8. Moreover, it will be assumedthat the orifices l7 and 18 are connected to a suitable source of fluidunder'pressure. Under these conditions, the traction ram is ready tooperate. The

keys l5 and movable traction device 13 are positioned as shown in FIG.6; then, fluid under pressure is delivered through orifice 17 intochamber 16a. As a consequence, the piston 12 is moved back into thedirection of the arrow F (FIG. 1). The keys 15 of traction device 13,whichare in frictional contact with the cables 5, are firstly retainedby these cables, so that they move to the position illustrated in thelocked by the retaining device 11, if thepiston 12'continues itsmovement in the direction of the arrow'F fthe keys I5 of traction block13 will move, as a consequence of their frictional engagement withcables 5, to the position illustrated in the same FIG. 8, and theassembly comprising the piston 12 and traction block 13, with its keys15, will continue its movement until it attains the position'shown inthe upper portion of FIG. 1 in which the piston 12 abuts against therear end of the intermediate bearing member 7. The cycle of theabove-described operations may then be repeated in order to exertanother traction on the cables, by switching'thesupply of fluid underpressure from orifice 18 to orifice 17, and then operating exactly asdescribed hereinabove. By performing a: certain number, of tractioncycles the anchoring device 6 eventually penetrates into the 'opening ofbearing plate 4 and the nut 8 can then be screwed on this anchoringdevice until. it engages the plate 4, so that the cable's5 canproperly'held in their taut condition. Then the ram 11 can be removed forperforming another prestressing operation, if required. However, toremove the ram, 11 it is necessary to take certain 'care. In fact, afterthe last traction stroke, the componentelements of the ram are in theposition shown in FIG.'7, so that the cablesec'-- I tions disposedbetween the anchoring device 6 and thekeys 15 of traction block 13 arestill strongly tensioned. Therefore, to prevent the cables 5 fromcarrying along by friction the keys 15 of retaining block 11 during thereturn stroke of piston 12 in the direction of the arrow F L which wouldcause these keys to be clamped on the cables and, therefore, prevent theremoval of the traction ram, the pair of lock pegs 31 are insertedbehind the grid 30 so that the latter can hold the keys 1 5 of retainingblock 11in their release position, as shown in the lower portion ofFIG. 1. Then fluid under pressure can be introduced through the orifice18 so as to move the piston 12 and the movable traction block 13 fromthe position shown in FIG. 7 to the position shown in FIG. 6. In thislast position, the

keys 15 of traction block 13 are pushed back by grid 29 to tions, itcould easily be modified with the view to utilize same as a step-by-stepdriving device for displacing a bulky assembly or a load attached in anysuitable manner to the body 10 of the ram in relation to one or aplurality of cables or to one or a plurality of parallel fixed bars orrods acting as rails. Under these conditions, the intermediate bearingmember 7 and grid 30 can be dispensed with, but the retaining device 11must nevertheless be properly connected to the body 10 of the tractionram. Moreover, the clamping members of the fixed retaining device 11 andof the movable traction device 13 must be designed to suit the numberand shape of the cables, strands, rods or bars acting as guide rails.

lclaim:

l. A power apparatus operating by successive steps, comprising a bodyformed with a cylindrical bore, a retaining device secured at one end tosaid body in a coaxial position in the bore thereof and having anexternal cylindrical surface of smaller diameter than said bore so as toprovide between its outer surface and the wall of said bore an annularspace closed on the side of the end of said retaining device secured tosaid body, an annular piston adapted to slide axially in said annularspace so as to separate therein two axially spaced annular chambers eachprovided with an inlet orifice for supplying fluid under pressurethereto, a coaxial tubular rod of said piston connected at one end tosaid piston and extending from said piston in the direction opposite tothat of said closed end of said annular space, a sealing member disposedbetween the inner wall of said bore of said body and the outer surfaceof the tubular piston rod for closing in a fluid-tight manner the otherend of said annular space, and a movable traction device aligned withsaid fixed retaining device and connected to the other end of saidtubular piston rod, and fixed retaining device and said movable tractiondevice being arranged with a view to receive axially therethrough atleast one elongated member of constant cross-sectional area, with whichthe power apparatus is adapted to co-operate, each one of said retainingand traction devices enclosing a set of clamping members coacting byfrictional contact with said elongated members, for releasing andautomatically gripping, respectively, said elongated member when a fluidunder pressure is delivered into one of said annular chambers and thepiston is moved in a first direction corresponding to a power stroke, soas to produce a relative movement between the power apparatus and saidelongated member, and vice-versa for automatically gripping andreleasing said elongated member, respectively, when said fluid underpressure is delivered into the other annular chamber and the pistontravels in a direction opposite to said first direction, whichcorresponds to an inoperative return stroke.

2. Power apparatus as set forth in claim 1, wherein said fixed retainingdevice and said movable traction device comprise each a hollowcylindrical body of which the inner surface is inclined in relation tothe axis of said cylindrical body and receives therein said set ofclamping members associated therewith, said assembly having an outersurface having the same inclination as the inner surface of the hollowcylindrical body, whereby a relative axial displacement of the set ofclamping members with respect to said hollow body is attended, accordingto the direction of said relative displacement, by the clamping orrelease of said elongated member by the clamping members.

3. Power apparatus as set forth in claim 2, wherein said inner inclinedsurface of said hollow body and said outer surface of set of clampingmembers associated therewith are shaped to correspond to internal andexternal screw threads, respectively, said threads comprising a frontface of relatively great width and slightly incllned in relation to theaxis of said hollow body, and a rear face of considerably shorter widthand steeper inclination in relation to said axis in comparison with saidfront face.

4. Power apparatus as set forth in claim 3, wherein each set of clampingmembers is designed for co-acting with a plurality of cables or barshaving a constant cross-sectional area and comprises in this case asmany identical clamping members as there are cables or rods, eachclamping member having sub stantially the shape of a cylinder sectorwith an external surface such that, when all the clamping members areassembled, the outer surface of their assembly as the shape of saidscrew threads, each clamping member further comprising in each one ofits lateral faces a longitudinal groove accomlodating the shape of acable or bar to be clamped, the grooves formed in the two registeringlateral surfaces of two adjacent clamping members being adapted toco-act for surrounding a same cable or bar.

5. Power apparatus as set forth in claim 4, wherein resilient returnmeans tending to move adjacent clampingmembers away from each other aredisposed between each pair of registering lateral faces of adjacentclamping members.

6. Power apparatus as set forth in claim 5, wherein said resilientreturn means consist of a corrugated spring steel blade of which thepeaks of the corrugations bear alternatively on said registering faces.

7. Power apparatus as set forth in claim 6, wherein said corrugatedblade is inserted in a pair of longitudinal grooves opening towards eachother, which are formed in said registering lateral faces respectively,parallel to said cable or barreceiving grooves, between said last-namedgrooves and the corresponding edges of said registering faces which areadjacent to the external surface of said clamping members, and thatmeans are provided for preventing any longitudinal displacement of saidblade in said grooves.

8. Power apparatus as set forth in claim 1, adapted for use as atraction ram for pulling the end of at least one cable extending througha member of body to be compressed and of which the opposite end isanchored to a first side of same member or body to be compressed, saidtraction ram bearing on a second side, opposite to said first side, ofsaid member or body to be compressed, and stop means provided forco-acting with said cable and said other side in order to keep saidmember or body to be compressed in its compressed condition when apredetermined tractive effort is applied to said cable, and wherein atubular bearing member constitutes the extension of the body of said rambeyond said end and bears against the other side of said member of bodyto be compressed, said tubular member comprising at least one relativelywide longitudinal slot permitting the access to said stop means.

9. A traction ram as set forth in claim 8, wherein a movable gridreceiving said cable therethrough and adapted to be brought intoengagement with the ends of the clamping members of the fixed retainingdevice in order to push same back to its release position is disposed onthe side of the end of said fixed device which is adjacent to the memberor body to be compressed, and wherein the other end of said fixedretaining device has secured thereto another grid against which theclamping members of the movable traction device are adapted to abut atthe end of the return stroke of said piston so as to be pushed back to arelease position, means being also provided for holding when desiredsaid movable grid in its position of engagement with the clampingmembers of the fixed retaining member and holding said clamping membersin their release position.

UNITED STATES PATENT OFFICE CERTIFICATE CF CORRECTION v Patent 3,653,634Dated- April 4 1972 Rene Behi Inventor(s) It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected a s shown below:

Inventor: RENE BEGHI, Bois Colombes,- France Assignee: SOCIETE DESGRANDS TRAVAUX DE MARSEILLE,

NANTERRE, FRANCE Signed and sealed this 3rd day of October- 1972.

(SEAL) Attest:

- RO-BER'I'. GOTTSCHALK USCGMM-DC 6037e-P6 I v.1. oovnmlnn "mums ovnc: 1"n o-su-u FORM 5 0-1050 (10-69}

1. A power apparatus operating by successive steps, comprising a bodyformed with a cylindrical bore, a retaining device secured at one end tosaid body in a coaxial position in the bore thereof and having anexternal cylindrical surface of smaller diameter than said bore so as toprovide between its outer surface and the wall of said bore an annularspace closed on the side of the end of said retaining device secured tosaid body, an annular piston adapted to slide axially in said annularspace so as to separate therein two axially spaced annular chambers eachprovided with an inlet orifice for supplying fluid under pressurethereto, a coaxial tubular rod of said piston connected at one end tosaid piston and extending from said piston in the direction opposite tothat of said closed end of said annular space, a sealing member disposedbetween the inner wall of said bore of said body and the outer surfaceof the tubular piston rod for closing in a fluid-tight manner the otherend of said annular space, and a movable traction device aligned withsaid fixed retaining device and connected to the other end of saidtubular piston rod, and fixed retaining device and said movable tractiondevice being arranged with a view to receive axially therethrough atleast one elongated member of constant cross-sectional area, with whichthe power apparatus is adapted to co-operate, each one of said retainingand traction devices enclosing a set of clamping members co-acting byfrictional contact with said elongated members, for releasing andautomatically gripping, respectively, said elongated member when a fluidunder pressure is delivered into one of said annular chambers and thepiston is moved in a first direction corresponding to a power stroke, soas to produce a relative movement between the power apparatus and saidelongated member, and vice-versa for automatically gripping andreleasing said elongated member, respectively, when said fluid underpressure is delivered into the other annular chamber and the pistontravels in a direction opposite to said first direction, whichcorresponds to an inoperative return stroke.
 2. Power apparatus as setforth in claim 1, wherein said fixed retaining device and said movabletraction device comprise each a hollow cylindrical body of which theinner surface is inclined in relation to the axis of said cylindricalbody and receives therein said set of clamping members associatedtherewith, said assembly having an outer surface having the sameinclination as the inner surface of the hollow cylindrical body, wherebya relative axial displacement of the set of clamping members withrespect to said hollow body is attended, according to the direction ofsaid relative displacement, by the clamping or release of said elongatedmember by the clamping members.
 3. Power apparatus as set forth in claim2, wherein said inner inclined surface of said hollow body and saidouter surface of set of clamping members associated therewith are shapedto correspond to internal and external screw threads, respectively, saidthreads comprising a front face of relatively great width and slightlyincllned in relation to the axis of said hollow body, and a rear face ofconsiderably shorter width and steeper inclination in relation to saidaxis in comparison with said front face.
 4. Power apparatus as set forthin claim 3, wherein each set of clamping members is designed forco-acting with a plurality of cables or bars having a constantcross-sectional area and comprises in this case as many identicalclamping members as there are cables or rods, each clamping memberhaving substantially the shape of a cylinder sector with an externalsurface such that, when all the clamping members are assembled, theouter surface of their assembly as the shape of said screw threads, eachclamping member further comprising in eacH one of its lateral faces alongitudinal groove accomlodating the shape of a cable or bar to beclamped, the grooves formed in the two registering lateral surfaces oftwo adjacent clamping members being adapted to co-act for surrounding asame cable or bar.
 5. Power apparatus as set forth in claim 4, whereinresilient return means tending to move adjacent clamping members awayfrom each other are disposed between each pair of registering lateralfaces of adjacent clamping members.
 6. Power apparatus as set forth inclaim 5, wherein said resilient return means consist of a corrugatedspring steel blade of which the peaks of the corrugations bearalternatively on said registering faces.
 7. Power apparatus as set forthin claim 6, wherein said corrugated blade is inserted in a pair oflongitudinal grooves opening towards each other, which are formed insaid registering lateral faces respectively, parallel to said cable orbar-receiving grooves, between said last-named grooves and thecorresponding edges of said registering faces which are adjacent to theexternal surface of said clamping members, and that means are providedfor preventing any longitudinal displacement of said blade in saidgrooves.
 8. Power apparatus as set forth in claim 1, adapted for use asa traction ram for pulling the end of at least one cable extendingthrough a member of body to be compressed and of which the opposite endis anchored to a first side of same member or body to be compressed,said traction ram bearing on a second side, opposite to said first side,of said member or body to be compressed, and stop means provided forco-acting with said cable and said other side in order to keep saidmember or body to be compressed in its compressed condition when apredetermined tractive effort is applied to said cable, and wherein atubular bearing member constitutes the extension of the body of said rambeyond said end and bears against the other side of said member of bodyto be compressed, said tubular member comprising at least one relativelywide longitudinal slot permitting the access to said stop means.
 9. Atraction ram as set forth in claim 8, wherein a movable grid receivingsaid cable therethrough and adapted to be brought into engagement withthe ends of the clamping members of the fixed retaining device in orderto push same back to its release position is disposed on the side of theend of said fixed device which is adjacent to the member or body to becompressed, and wherein the other end of said fixed retaining device hassecured thereto another grid against which the clamping members of themovable traction device are adapted to abut at the end of the returnstroke of said piston so as to be pushed back to a release position,means being also provided for holding when desired said movable grid inits position of engagement with the clamping members of the fixedretaining member and holding said clamping members in their releaseposition.